[FLASH-USERS] Adding viscous term in the momentum equation

[Klaus Weide]

On Fri, 12 Jun 2020, Acharya, Nitish wrote:

> I figured FLASH solves only the non-viscous Euler equations for 
> simulating HED experiments. I plan to solve a complete Navier Stokes 
> Equation for a Laserslab problem by explicitly defining a constant 
> viscosity coefficient for materials. From what I understand, I might 
> have to add a viscous term in the momentum equation and modify the hydro 
> unit in FLASH. How convenient is it to implement this? What should be 
> the general approach to add this extra term in the hydro solver? I would 
> really appreciate any sort of help here?

As Rodrigo Fernandez already pointed out, you can use the "flux-based" 
part of the "Diffuse" unit for your purpose. You will need to include

  physics/Diffuse/DiffuseFluxBased

in your configuration, as well as an implementation of the Viscosity unit, 
and set appropriate runtime parameters. Hopefully the User's Guide can 
help you further.

Keep in mind that this is an explicit implementation; FLASH currently does 
not provide an implicit (or semi-implicit) solver for viscosity. So your 
time step may have to become significantly smaller than what you are used 
to.

Klaus